Composites incorporating nano-scale particles are well known. Nanomaterials is a field that takes a materials science-based approach on nanotechnology. Materials incorporating nanoscale structures may have unique properties stemming from morphological features with nanoscale dimensions. In this regard, the term “nanoscale” is often defined as smaller than 1 nanometer in at least one dimension. However, in practice and in existing commercial products, some nanostructures may have their smallest dimensions significantly larger than 1 nanometer. On the other hand, recent nanotechnology development has also made some structures with dimensions substantially less than 1 nanometer. Hence, for purposes of this disclosure, it is to be understood that “nanoscale” is defined as from 0.1 nanometer to 1000 nanometers. A “nanoscale material” is a natural, incidental or manufactured material containing nanoscale structures “nanostructrures” such as fibers, particles and the like, in an unbound state or as an aggregate or agglomerate.
An important aspect of nanotechnology is the vastly increased ratio of surface area to volume present in many nanoscale materials, which makes possible new quantum mechanical effects. One example is the “quantum size effect” where the properties of solids having particles dispersed within a matrix may be altered as a result of significant reductions in particle size. By way of example only, characteristics such as electrical conductivity and optical fluorescence may be influenced significantly by the presence of nanostructures due to the dramatically increased surface area to volume ratio of those structures. These significant influences typically do not come into play by going from macro to micro dimensions. However, they become pronounced when the nanoscale size range is reached.
A certain number of physical properties also alter with the change to nanoscale systems. By way of example only, nanostructures within a bulk material can strongly influence mechanical properties of the material, such as stiffness or elasticity. In some applications of use, it has been found that traditional polymers can be reinforced by nanostructures resulting in novel materials which can be used as lightweight replacements for metals. Such nanotechnologically enhanced materials may enable a weight reduction accompanied by an increase in stability and improved functionality. Other functions such as catalytic activity for treatment of biomaterials also may be strongly influenced by the presence of nanoscale structures.
Several types of nanomaterials have been used to create advanced composite structures. Industries desiring high performance, light weight structures have increasingly focused on fiber reinforced plastic (FRP). Such FRP materials typically include a multiplicity of micro-scale fibers having an effective diameter ranging ranges from about 1 micrometer to 1000 micrometers. In practice, such micro-scale fibers can be orientated in any preferred in-plane direction within the FRP laminate to reinforce the strength of the FRP laminate in the preferred in-plane direction. Some special FRP laminate parts may have the micro-scale fibers not orientated in any in-plane direction due to the special design needs or due to the non-uniform thickness of the FRP laminate parts such as a tapered geometry or the like. FRP materials are considered superior to their metallic counterparts due to their high strength-to-weight ratios. However, improvements in the durability and damage tolerance of these light-weight materials are still desired because of the relative weakness of the binding polymer matrix in FRP laminates. In this regard, the weakness of most FRP laminates is caused by the lack of effective fiber reinforcement in the direction perpendicular to the local micro-scale fiber orientation. For example, in a typical FRP laminate with micro-scale fibers orientated in the in-plane direction, the weak direction is the through-thickness direction. As a result, many through-thickness-direction related properties of FRP laminates are dominated by the properties of the polymer matrix, rather than by the fibers.
Several studies have demonstrated that the appropriate addition of nanostructures such as nanofibers, nanotubes, nanorods, or nanoplatelets to a polymer matrix can drastically enhance the polymer matrix performance. When introducing nanostructures to improve performance in a FRP material, there are two primary processes which can be used to improve a multi-scale composite laminate: (1) targeted reinforcement of the fiber/matrix interface; and (2) the general reinforcement of the bulk matrix. Reinforcement of the interface may be achieved by the deposition of nanostructures on the surface of the continuous fiber systems. Exemplary deposition processes include electrophoresis, chemical vapor deposition, and sizing. Bulk matrix reinforcement is typically done by adding nanostructures into the matrix solution before impregnation of the micro-scale fiber system thereby forming a so called “nanocomposite”.
Despite the advancements made in the synthesis of these nanocomposites, the technology remains at a very early stage where systematic improvement has yet to be achieved. It is believed that the lack of high-aspect-ratio nanostructure orientation control (i.e., alignment) certainly diminishes the effectiveness of the high-aspect-ratio nanostructure reinforcement in multi-scale composites. Moreover, deposition technologies such as chemical vapor deposition (CVD) and the like are not a particularly good solution due to cost and complexity.
Examples of known high-aspect-ratio nanostructures which may be used to adjust the character of a matrix include carbon nanotubes, fibrous nanocarbons, metal nanorods, nanoclays, and graphite nanoplatelets. It is known that the alignment of high-aspect-ratio nanostructures in water or neat polymer solution can be achieved by electric or magnetic field. However, as best understood, no technique has been identified to use electric or magnetic field to achieve alignment of high-aspect-ratio nanostructures in FRP or other micro-scale composites. Without being limited to a particular theory, it is suspected that one possible reason for the inability to use electric or magnetic field treatment to align high-aspect-ratio nanostructures in FRP materials may be the undesired interference from the existing micro-scale fiber arrays in the FRP matrix.
In this disclosure the following definitions apply:
A “nanostructure” is a structure that has at least one of its dimensions within the aforesaid nanoscale range (i.e., from 0.1 nanometer to 1000 nanometers);
A “high-aspect-ratio nanostructure” is a nanostructure wherein at least one of its dimensions is at least five times longer than its smallest dimension;
A “fiberous nanocarbon” is a long-shaped, high-aspect-ratio nanostructure with a composition having a majority amount of carbon and with its effective diameter being within the aforesaid nanoscale range (i.e., from 0.1 nanometer to 1000 nanometers).